Stem cells are unspecialized cells that can differentiate into specialized cell types and have potential uses in treating diseases. There are two main types of stem cells: embryonic stem cells which are derived from embryos and adult stem cells which come from adult tissues. Embryonic stem cells can become any cell type but their use is controversial due to ethical issues. Adult stem cells are more limited in their differentiation potential but do not pose the same ethical concerns. The author supports stem cell research but believes it should be regulated, especially regarding the source of embryonic stem cells.